High Attack Rate Research Articles

Control of tungiasis through intermittent application of a plant-based repellent: an intervention study in a resource-poor community in Brazil.

BackgroundTungiasis, an ectoparasitosis caused by the female sand flea Tunga penetrans, is an important health problem in many impoverished communities in the tropics. Sand flea disease is associated with a broad spectrum of clinical pathology and severe sequels are frequent. Treatment options are limited.Methodology/Principal FindingsWe assessed the effectiveness of the intermittent application of the plant-based repellent Zanzarin to reduce infestation intensity and tungiasis-associated morbidity in a resource-poor community in Brazil, characterized by a very high attack rate. The study population was randomized into three cohorts. Initially, during a period of four weeks, the repellent was applied twice daily to the feet of all cohort members. This reduced the number of embedded sandfleas to 0 in 98% of the participants. Thereafter members of cohort A applied the repellent every second week twice daily for one week, members of cohort B every fourth week for one week, and members of cohort C served as controls. Infestation intensity and tungiasis-associated morbidity were monitored during five months. The intermittent application of Zanzarin for one week every second week significantly reduced infestation intensity from a median 4 lesions (IQR 1–9) during the whole transmission season. In contrast, in cohort B (application of the repellent every fourth week) the infestation intensity remained twice as high (median 8 lesions, IQR 9–16; p = 0.0035), and in the control cohort C 3.5 times as high (median 14 lesions; IQR 7–26; p = 0.004 during the transmission season). Tungiasis-related acute pathology remained very low in cohort A (median severity score 2; IQR 1–4) as compared to cohort B (median severity score 5; IQR 3–7; p<0.001), and control cohort C (median severity score 6.5; IQR 4–8; p<0.001).Conclusions/SignificanceOur study shows that in a setting with intense transmission, tungiasis-associated morbidity can be minimized through the intermittent application of a plant-based repellent.

Influenza vaccine coverage among children under the age of 5 years in Poland during 2004-2008

IntroductionInfluenza is a considerable health problem all over the world. The most important group for influenza vaccination are children: the highest attack rate during community out-breaks of influenza can be found among school-aged children or their family members; children bear a considerable risk for complications due to influenza, leading to an increased need for healthcare resources (including hospitalization). The high level of vaccine coverage among school children could provide protection against influenza among households and could reduce mortality rates among older individuals.ObjectiveThe aim of this study was to estimate the influenza vaccine coverage among children younger than 5 years and to find any trends in influenza vaccine coverage in 2004-2008 in Poland.Material and methodsOfficial data (number of administrated vaccines and the age of vaccinated individuals) collected by the National Institute of Hygiene, the National Institute of Public Health, and the Central Statistical Office in Poland were analyzed. This data are reported by physicians and collected from reports prepared annually by the Sanitary-Epidemiological Stations at a local level. The vaccine coverage rate was calculated as a percentage of vaccinated individuals among all children under the age of 5 years.ResultsThe influenza vaccine coverage among children younger than 5 years varied from 1% (2007 and 2008) to 1.9% (2005). The proportion of vaccinated children aged less than 5 compared with the total number of flu shots administrated irrespective of age also varied from 1.4% (2007) to 2% (2005).ConclusionsThe influenza vaccination coverage among Polish children aged less than 5 years is low and has persisted at the same level. More educational activities directed both to patients (parents) and healthcare workers would be needed to improve a general knowledge about influenza vaccination benefits among young children.

Salticid predation as one potential driving force of ant mimicry in jumping spiders.

Many spiders possess myrmecomorphy, and species of the jumping spider genus Myrmarachne exhibit nearly perfect ant mimicry. Most salticids are diurnal predators with unusually high visual acuity that prey on various arthropods, including conspecifics. In this study, we tested whether predation pressure from large jumping spiders is one possible driving force of perfect ant mimicry in jumping spiders. The results showed that small non-ant-mimicking jumping spiders were readily treated as prey by large ones (no matter whether heterospecific or conspecific) and suffered high attack and mortality rates. The size difference between small and large jumping spiders significantly affected the outcomes of predatory interactions between them: the smaller the juvenile jumping spiders, the higher the predation risk from large ones. The attack and mortality rates of ant-mimicking jumping spiders were significantly lower than those of non-ant-mimicking jumping spiders, indicating that a resemblance to ants could provide protection against salticid predation. However, results of multivariate behavioural analyses showed that the responses of large jumping spiders to ants and ant-mimicking salticids differed significantly. Results of this study indicate that predation pressure from large jumping spiders might be one selection force driving the evolution of nearly perfect myrmecomorphy in spiders and other arthropods.

Investigation of an epidemic of Hepatitis E in Nellore in south India

To determine the incidence of acute hepatitis because of hepatitis E virus (HEV) and the source of the epidemic in Nellore in south India in 2008. Anti-HEV IgM ELISA and RT-PCR for HEV-RNA were carried out on blood and stool samples from patients with acute hepatitis presenting to different hospitals in the city. The city was divided into 33 clusters, and 20 families from each cluster were systematically interviewed to determine the incidence of hepatitis E in the city. The survey was conducted on 2685 residents of 673 households from 24th November to 4th December 2008. The overall incidence of hepatitis was 5.7% (152/2685), i.e. an estimated 23,915 persons in the city were affected. There were two deaths because of acute hepatitis in the population surveyed translating to an estimated 315 deaths. Men had higher attack rates than women (7.8%vs. 3.5%) and young adults compared to children under 5 years (6.9%vs. 2.9%). Families drinking water from the pumping station at Bujjamarevu had the highest attack rate of 54.5% (39.8-69.2%). HEV IgM antibodies were present in 80/100 plasma samples tested. HEV-RNA was detected in 43/100 individuals tested, and isolates were characterized as genotype 1 by sequencing. Sewage draining into the river close to the pumping stations and broken pipelines crossing sewage drains may have triggered this large outbreak.

Dose–response modeling of Salmonella using outbreak data

Salmonella is a key human pathogen worldwide, most often associated with food poisoning incidences. There is a small number of predominant serotypes found in human cases. The role of exposure in the epidemiology of Salmonella can be explained using dose–response assessment both for infection and acute enteric illness. Dose–response studies are traditionally based on human challenge experiments but an alternative is to use outbreak data. Such data were collected from the published literature which included estimates of the dose ingested and the attack rate. Separate dose–response models for infection and illness given infection were fitted using a multi-level statistical framework. These models incorporated serotype and susceptibility as categorical covariates, and adjusted for heterogeneity in exposure. The results indicate that both the risk of infection and the risk of illness given infection increase with dose. The dose–response model incorporating data from all outbreaks had an infection ID50 of 7 CFU's and illness ID50 of 36 CFUs. This is indicative of much higher infectivity and pathogenicity compared with feeding studies of healthy human volunteers with laboratory adapted strains. No differences were found in the outbreak models between serotypes and susceptibility categories. However, for serotypes other than S. Enteritidis or S. Typhimurium, results indicate that a minor proportion of individuals exposed will not fall ill even at high doses. The dose–response relations indicate that outbreaks are associated with higher doses making it more likely to have a higher attack rate. Applications of the dose–response model in outbreak situations where either dose or attack rate is missing were successfully used to clarify the epidemiology. Finally, the dose–response models described here can be readily used in quantitative microbiological risk assessment to predict human infection and illness rates. A simple Excel spreadsheet implementing the model has been prepared and is available from the authors.

An outbreak of measles among unvaccinated migrant population in Zhejiang province, from June to August, 2010

On July 6, 2010, the parents of a patient with confirmed measles reported several suspected measles patients with fever and rash in their village. An investigation was carried out to verify and understand the cause of the outbreak. Several suspected cases had an onset of fever and rash in this and other neighboring villages during June 1 to August 3, 2010. A confirmed case was a suspected case with measles-specific IgM identified in the serum. We conducted door-to-door visits and searched the Chinese Center for Disease Control and Prevention Information System to identify cases, also conducted a retrospective cohort study among migrant children aged 8 months-14 years to identify risk factors related to measles. We identified 19 measles cases (17 confirmed case, 2 suspected cases) in the village, and all of them were migrants. Children aged 1-2 years had the highest attack rate (13%). The primary case-patient had onset on the day she arrived in this village (June 4, 2010). Caretakers from an unlicensed private clinic were providing service in the village but did not report the outbreak to the public health authority. The outbreak was identified only after receiving a report from the parents of one of the patients, by that time the outbreak had lasted for one month. The measles vaccine coverage rate was 81% among the 315 migrant children aged 8 months-14 years. Among the 61 unvaccinated children, those who reportedly being contacted a measles patient had a higher attack rate (14/16, 88%) than those who did not (2/45, 4.4%) (Relative risk = 20, Fisher's exact 95% confidence interval: 5.7-94). The low measles vaccine coverage among migrant children and lack of measures taken on the incident, timely isolation diagnosis/reporting by the caretakers from the unlicensed private clinic etc. had contributed to this prolonged outbreak. Measures need to be taken to improve the immunization services for migrant populations and to enhance measles surveillance programs in the area.

Is &lt;i&gt;Vibrio fluvialis&lt;/i&gt; Emerging As a Pathogen with Epidemic Potential in Coastal Region of Eastern India Following Cyclone &lt;i&gt;Aila&lt;/i&gt;?

An isolated area with diarrhoea epidemic was explored at Pakhirala village of the Sundarbans, a coastal region of South 24 Parganas district of West Bengal, eastern India. The Pakhirala village was surrounded by other villages affected by a similar epidemic. The affected villages experienced this epidemic following the cyclone Aila, which had hit the coastal region of the Sundarbans in eastern India. In Pakhirala, the situation was the worst. Within a span of six weeks (5 June-20 July 2009), 3,529 (91.2%) of 3,871 residents were affected by watery diarrhoea. Of all the cases (n = 3,529), 918 (26%) were affected by moderate to severe diarrhoea. In other villages, 28,550 (70%) of the 40,786 people were affected; of them, 3,997 (14%) had moderate to severe watery diarrhoea. The attack rate and the severity of the cases were significantly higher in Pakhirala village compared to other affected villages. The laboratory results revealed that Vibrio fluvialis was the predominant pathogen in Pakhirala village (5 of 6 laboratory-confirmed organisms) whereas Vibrio cholerae O1 Ogawa was the predominant pathogen in other villages of Gosaba block (7 of 9 bacteriologically-confirmed organisms). This result indicates that V fluvialis behaves more aggressively than V cholerae O1 in an epidemic situation with a higher attack rate and a different clinical picture. An in-depth study is required to explore its pathogenicity in detail, geographical distribution, and possible control measures, including development of specific vaccine preparation and determination of its efficacy.

Genome sequences of Human Adenovirus 14 isolates from mild respiratory cases and a fatal pneumonia, isolated during 2006-2007 epidemics in North America

BackgroundHuman adenovirus 14 (HAdV-14) is a recognized causative agent of epidemic febrile respiratory illness (FRI). Last reported in Eurasia in 1963, this virus has since been conspicuously absent in broad surveys, and was never isolated in North America despite inclusion of specific tests for this serotype in surveillance methods. In 2006 and 2007, this virus suddenly emerged in North America, causing high attack rate epidemics of FRI and, in some cases, severe pneumonias and occasional fatalities. Some outbreaks have been relatively mild, with low rates of progression beyond uncomplicated FRI, while other outbreaks have involved high rates of more serious outcomes.Methodology and FindingsIn this paper we present the complete genomic sequence of this emerging pathogen, and compare genomic sequences of isolates from both mild and severe outbreaks. We also compare the genome sequences of the recent isolates with those of the prototype HAdV-14 that circulated in Eurasia 30 years ago and the closely related sequence of HAdV-11a, which has been circulating in southeast Asia.ConclusionsThe data suggest that the currently circulating strain of HAdV-14 is closely related to the historically recognized prototype throughout its genome, though it does display a couple of potentially functional mutations in the fiber knob and E1A genes. There are no polymorphisms that suggest an obvious explanation for the divergence in severity between outbreak events, suggesting that differences in outcome are more likely environmental or host determined rather than viral genetics.

Surveillance of the 2009 flu pandemic in Belgium

Surveillance of the 2009 flu pandemic in Belgium

On the risk of extinction of a wild plant species through spillover of a biological control agent: Analysis of an ecosystem compartment model

Invasive plant species can be controlled by introducing natural enemies (insect herbivores) from their native range. However, such introduction entails the risk that the introduced herbivores attack indigenous plant species in the area of introduction. Here, we study the effect of spillover of a herbivore from a managed ecosystem compartment (agriculture) to a natural compartment (non-managed) and vice versa. In the natural compartment, an indigenous plant species is attacked by the introduced herbivores, whereas another indigenous plant species, which competes with the first, is not attacked. The combination of competition and herbivory may result in extinction of the attacked wild plant species. Using a modelling approach, we determine model parameters that characterize the risk of extinction for a wild plant species. Risk factors include: (1) a high attack rate of the herbivores on the wild non-target species, (2) niche overlap expressed as strong competition between the attacked non-target species and its competitor(s), and (3) factors favouring large spillover from the managed ecosystem compartment to the natural compartment; these include (3a) a high dispersal ability, and (3b) a moderate attack rate of the introduced herbivore on the target species, enabling large resident populations of the insect herbivore in the managed compartment. The analysis thus indicates that a high attack rate on the target species, which is a selection criterion for biocontrol agents with respect to their effectiveness, also mitigates risks resulting from spillover and non-target effects. While total eradication of an invasive plant species is not possible in the one-compartment-one-plant-one-herbivore system, natural enemy spillover from a natural to a managed compartment can make the invasive weed go extinct.

Bacterial Pathogens in Ixodid Ticks from a Piedmont County in North Carolina: Prevalence of Rickettsial Organisms

In North Carolina, reported human cases of tick-borne illness, specifically Rocky Mountain spotted fever, have escalated over the past decade. To determine the relative abundance of vectors and to estimate the risk of acquiring a tick-borne illness in peri-residential landscapes, ticks were collected in Chatham County, a typical Piedmont county and, samples of the ticks were tested for infection with selected bacterial pathogens using real-time quantitative polymerase chain reaction assays. Ticks (n = 3746) were collected by flagging vegetation at 26 sites from April to July 2006. The predominant questing tick was Amblyomma americanum (98.5%) with significantly fewer Dermacentor variabilis (1.0%) and Ixodes scapularis (0.5%) collected. Spotted fever group (SFG) rickettsiae were detected in 68.2% of 1590 A. americanum with 56.4% of the molecular isolates identified as Rickettsia amblyommii, an informally named member of the SFG rickettsiae. Comparatively, smaller numbers of A. americanum contained Ehrlichia chaffeensis (1.8%) and Borrelia lonestari (0.4%). Of 15 I. scapularis nymphs tested, 6 (40%) were positive for Borrelia burgdorferi sensu lato. Seven (19.4%) of 36 adult D. variabilis tested positive for Rickettsia montanensis, 4 (11.1%) were positive for R. amblyommii, and 5 (13.9%) were infected with unidentified species of SFG rickettsiae. The tick population in Chatham County contains a diverse array of microbes, some of which are known or potential pathogens. Highest attack rates would be expected from A. americanum ticks, and highest potential risk of infection with a tick-transmitted agent would be to rickettsial organisms, particularly R. amblyommii. Accordingly, longitudinal eco-epidemiology investigations are needed to determine the public health importance of A. americanum infected with rickettsial organisms.

Dynamics of infectious disease transmission by inhalable respiratory droplets.

Transmission of respiratory infectious diseases in humans, for instance influenza, occurs by several modes. Respiratory droplets provide a vector of transmission of an infectious pathogen that may contribute to different transmission modes. An epidemiological model incorporating the dynamics of inhalable respiratory droplets is developed to assess their relevance in the infectious process. Inhalable respiratory droplets are divided into respirable droplets, with droplet diameter less than 10 microm, and inspirable droplets, with diameter in the range 10-100 microm: both droplet classes may be inhaled or settle. Droplet dynamics is determined by their physical properties (size), whereas population dynamics is determined by, among other parameters, the pathogen infectivity and the host contact rates. Three model influenza epidemic scenarios, mediated by different airborne or settled droplet classes, are analysed. The scenarios are distinguished by the characteristic times associated with breathing at contact and with hand-to-face contact. The scenarios suggest that airborne transmission, mediated by respirable droplets, provides the dominant transmission mode in middle and long-term epidemics, whereas inspirable droplets, be they airborne or settled, characterize short-term epidemics with high attack rates. The model neglects close-contact transmission by droplet sprays (direct projection onto facial mucous membranes), retaining close-contact transmission by inspirable droplets.

Multiplexed Luminex xMAP Assay for Detection and Identification of Five Adenovirus Serotypes Associated with Epidemics of Respiratory Disease in Adults

Several serotypes of human adenovirus (HAdV) cause acute respiratory disease (ARD) among healthy adults, sometimes generating broad outbreaks with high attack rates and occasional fatalities. Timely serotype identification provides valuable epidemiological information and significantly contributes to prevention (vaccination) strategies. The prevalence of specific serotypes causing ARD varies geographically. HAdV-3, HAdV-4, HAdV-7, HAdV-14, and HAdV-21 are the serotypes most commonly found in adult populations in the Western Hemisphere. Unfortunately, conventional serotype identification is a tedious process which can take a week or longer. For this reason, new molecular methods for serotype identification are needed. Commercially available rapid antigen and PCR assays for the detection of HAdV are universal but do not distinguish between the different serotypes. We describe the development of a sensitive and specific multiplex assay capable of identifying serotypes 3, 4, 7, 14, and 21. Two sets of primers were used for nonspecific (universal) PCR amplification, and serotype-specific probes coupled to Luminex tags were used for target-specific extension (TSE). PCR and TSE primers were designed using known hexon gene sequences of HAdV. The TSE products of HAdV-3, HAdV-4, HAdV-7, HAdV-14, and HAdV-21 were correctly identified using the Luminex xMAP fluid microsphere-based array system. No cross-reactivity with other respiratory pathogens or other HAdV serotypes was observed. This multiplexed assay can be expanded to include more serotypes and will allow broad and rapid detection and identification of adenoviral serotypes in a high-throughput environment.

Evidence of Person‐to‐Person Transmission of Hepatitis E Virus during a Large Outbreak in Northern Uganda

Outbreaks of infection with hepatitis E virus (HEV) are frequently attributed to contaminated drinking water, even if direct evidence for this is lacking. We conducted several epidemiologic investigations during a large HEV infection outbreak in Uganda. Of 10,535 residents, 3218 had HEV infection; of these, 2531 lived in households with >1 case. HEV was not detected in drinking water or zoonotic sources. Twenty-five percent of cases occurred > or = 8 weeks after onset of hepatitis in an index case in the household. Households with > or = 2 cases were more likely to have a member(s) who attended a funeral, had close contact with a jaundiced person, or washed hands in a common basin with others (P < .05 for all). A high attack rate in households, lack of a common source of infection, and poor hygienic practices in households with > or = 2 cases suggest person-to-person transmission of HEV during this outbreak.

Influenza A(H1N1)2009 in the French Pacific territories: assessment of the epidemic wave during the austral winter

AbstractThe three French territories in the Pacific (New Caledonia [NC], French Polynesia [FP] and Wallis and Futuna [WF]) have been affected by an outbreak of influenza A(H1N1)2009 during the austral winter of 2009. This wave of influenza-like illness was characterized by a short duration (approximately 8 weeks) and high attack rates: 16–18% in NC and FP, 28% in Wallis and 38% in Futuna. The number of infected patients requiring hospitalization in critical care services and the number of deaths were, respectively, 21 and 10 in NC and 13 and 7 in FP (none in WF). Diabetes, cardiac and pulmonary diseases, obesity in adults, neuromuscular diseases in children, and Oceanic origin were frequently observed among severe cases and deaths. A significant proportion of the population remains susceptible to A(H1N1)2009, making the occurrence of a second wave likely. A state of preparedness and control efforts must be implemented, based on preventive measures (immunization), as well as combined clinical and virological surveillance and health organization.

Types of infectious outbreaks and their impact in elderly care facilities: a review of the literature

infectious outbreaks in long-term care facilities (LTCFs) tend to have a significant impact on infection rates and mortality rates of the residents. this review aimed to update the information on pathogens identified in such outbreaks and to try to explore indicators that reflect the impact of outbreaks among residents and health care workers (HCWs). MEDLINE (1966-2008) was used to identify outbreaks using the following thesaurus terms: 'Cross-Infection', 'Disease Outbreaks', 'Urinary-Tract Infections' and 'Blood-Borne Pathogens'. Elderly care facilities were identified with the following thesaurus terms: 'Long-Term Care', 'Assisted-Living Facilities', 'Homes for the Aged' and 'Nursing Homes'. Age category was limited using 'Aged'. thirty-seven pathogens were associated with 206 outbreaks. The largest number of reported outbreaks by a single pathogen involved the influenza virus, followed by noroviruses. Among residents, the highest median attack rate for respiratory infection outbreaks was caused by Chlamydia pneumoniae (46%), followed by respiratory syncytial virus (40%). In gastrointestinal tract infection outbreaks, high median attack rates were caused by Clostridium perfringens (48%) and noroviruses (45%). Outbreaks with high median case fatality rates were caused by Group A Streptococci (50%) and Streptococcus pneumoniae (44%). High median attack rates for HCWs were caused by C. pneumoniae (41%), noroviruses (42%) and scabies (36%). a variety of infectious agents were identified as the cause of outbreaks in the elderly and HCWs in LTCFs. Attack rates and case fatality rates are useful indicators for setting priorities for education and prevention of the outbreaks.

Age, influenza pandemics and disease dynamics

The world is currently confronting the first influenza pandemic of the 21st century [caused by a novel pandemic influenza A (H1N1) virus]. Earlier pandemics have been characterized by age distributions that are distinct from those observed with seasonal influenza epidemics, with higher attack rates (and correspondingly increased proportionate or relative mortality) in younger individuals. While the genesis of protection against infection in older individuals during a pandemic is uncertain, differential vulnerability to infection by age has important implications for disease dynamics and control, and for choice of optimal vaccination strategies. Age-related vulnerability to infection may explain differences between school- and community-derived estimates of the reproductive number (R) for a newly emerged pandemic strain, and may also help explain the failure of a newly emerged influenza A (H1N1) virus strain to cause a pandemic in 1977. Age-related factors may also help explain variability in attack rates, and the size and impact of influenza epidemics across jurisdictions and between populations. In Canada, such effects have been observed in the apparently increased severity of outbreaks on Indigenous peoples' reserves. The implications of these patterns for vaccine allocation necessitate targeted research to understand age-related vulnerabilities early in an influenza pandemic.

Investigation of extended-spectrum beta-lactamase-producingKlebsiella pneumoniaeoutbreaks in Hungary between 2005 and 2008

Fourteen outbreaks in Hungary between 2005 and 2008 caused by extended-spectrum beta-lactamase-producing Klebsiella pneumoniae (ESBL-KP) were epidemiologically investigated and the isolated pathogens were characterized by molecular techniques. Ten of the fourteen outbreaks occurred in adult wards and four in neonatal units affecting a total number of 73 patients. The 54% [40] of the patients developed bloodstream infections and 21.9%-21.9% [16] pneumonia and surgical site infections, respectively. The overall rate of mortality proved high: 36.9% [27]. Outbreaks in adults affected more patients, had higher attack rates, were more prolonged in duration and had a 6.9-fold higher mortality rate than outbreaks observed in neonates. The outbreaks in neonates were caused by SHV-type ESBL-producing klebsiellae, while in the "adult outbreaks" exclusively CTX-M-type ESBL-KP strains were involved. While the outbreak strains isolated from neonatal units could be assigned to a variety of pulsotypes, the previously described K. pneumoniae epidemic clones, ST15 and ST147, could be identified among the pathogens causing outbreaks in adult units.

Mumps outbreak in a highly vaccinated student population, The Netherlands, 2004

In September 2004 a mumps outbreak occurred at an international hotel school in The Netherlands. We investigated this outbreak to identify risk factors for mumps. There were 105 mumps cases (overall mumps attack rate (AR) 12% (95% CI: 10–15%)). The AR for Dutch vaccinated and unvaccinated participants was 12% (95% CI: 10–15%) and 15% (95% CI: 3–42%), respectively. Independent risk factor was mumps contact. Explanations for the relatively high AR among vaccinated participants include primary vaccine failure, waning immunity and incomplete vaccine-induced immunity in the context of high mumps virus exposure in a school party and a crowded boarding school.

Cybercrime – A game of cat and mouse in 2009

Last year saw the rapid evolution of complex security challenges. The internet engineering and security communities struggled against a wide range of threats including high DDoS attack rates, IPv6 adoption as well as the growing complexity of cloud and distributed infrastructures. Arbor Network's fifth annual 'Worldwide Infrastructure Security Report' (WWIR), a year long industry-wide operational security survey found some startling statistics and trends.